Process for purifying sodium stannate solution



Patented Aug. 21, 1928.

UNITED STATES PATENT OFFICE.

CHESTER L. READ, RAHWAY, AND BERRY MARVEL OHARRA, OF WESTFIELD,-J

NEW JERSEY, ASSIGNORS TO AMERICAN SMELTING AND REFINING COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

PROCESS FOR PURIFYING SODIUM STANNATE SOLUTION.

No Drawing.

' from any process in which alkali-metal stannates are produced, such as the refining of lead by treatment with caustic soda andsodium nitrate. .Such solutions usually contain, in addition to the stannates, salts of other metals such as lead, copper and similar metals and of antimony selenium and tellurium, which are the cause of great difliculties in thetreatment of the solution to recover the tin, making it impossible to secure firm, ad-

herent, non-spongy depositsof tin by the electrolytic process, as a result of wlnch large amounts ofthe deposited vtin are oxid zed and wastedinmelting down.

Bythe present invention a method is provided for the removal of these impurities which is simple inoperation, economical in practice, and which may be carried out wlth inexpensive equipment.

By this invention it is possible toenrich the solution in tin to an extent equivalent to a portion of the impurity metals remoyed, and to promote the recovery of the tin 1n a highly purified state and of the best quality. The recovery of by-products which would otherwise be lost, and which may be converted into useful and marketable products by suitable treatment, is made possible by this invention. I

The invention broadly consists in subjecting the alkali-metal stannate solution con:

taining impurities to the action of an alkali sulphide and of tin in an oxidizable condition in sufficient quantities to precipitate the impurity metals from the solution.

I In general the process'consists in adding r. the purifying reagents "to the solution, heating the mixture to suitable temperature and agitating or stirring it forasuflicient length of time to assure complete precipitationof the impurities in. a form easily separable from the solution by filtration or other suit-' able means. The purified solution may then be eleetrolyzedmnd ffirm, dense, non-spongy Application filed July 3,

, fere with the next step;

1926. 1 Serial No. 120,520.

deposits of tin secured, which may be melted with practically no oxidation of the metal. The impurities, after'removal from the solution, may also be subjected to suitable treatment to convert them into useful products.

The invention further consists in the new and novel features of operation and the new and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims. One method of practicing the invention is to add to the alkali-metal stannate solution a quantity of sodium sulphide, or other alkali sulphide, equivalent to the amount of lead,

copper and similar metals present in the solution. The amount required may be: determined by treating a measured quantity of the solution repeatedly with small measured may be coldduring this treatmenubut preferably it is heated to between degrees C. and the boiling point, as by so doing the alkali sulphide not only precipitates the im purities mentioned above but also 'tends'to reduce and render harmless any nitrates'that may be present. The impurities precipitated by the alkali sulphide may, if desired,

nowbe separated from the solution, as by filtration, but their presence will not inter- To I the solution, still Ymaintained at] or heated to between 70 degrees C. and its boiling point, is added finely divided metallic tin or stannous chloride, or tin in anoxidizable condition in any desired form,and the st'ir- "ring or agitation is continued. Under these conditions of temperature and agitation, the

antimony, selenium and tellurium are displacedfromthesolutionby the added tin,

the solution therebyv becoming enriched in tin to anfequivalent extent. 2 A The agitation andadd t on "of reagent maybe repeated, if necessary,uht1l all of the antimony, selenium and tGllU'IiLIIIl have been displaced from the solution as precipitates. I i

The precipitated impurities, including those precipitated in the first step if these have not already been remevemim some metals or to convert them into useful compounds. V

The purifiedsolution, whilestill hot, may be, electrolyzed. in the usual, manner, and, oiving to the absence of impurities which would, harmifully affect thistreatment,

smooth, firm deposits of tin of extreme purity areireadilyobtained. p

fAfmodified inethod in which the inventionma-y be practicedcoinprises adding the required amounts o t' alkali sulphide and tin or stannous chloride were hot solution at "one and the same time, and agitating the moved. The action of one reagent has no I mixture untilall of the impuritiesare reharmful effect on the other. By this method the time required for the treatment is somewhat less than When the treatment'i's made initivosteps; i

o By means of tliis processit is apparent that deleterioussubstances may be readily removed from alkali-metal 's'tannate solutions, so that tinof extreme purity maybe recovered from them. At the same time, by this process the solutions is enriched in tin, making the 'electrolyzing easier.

The absence of deleterious impurities during the electrolyzing makes it possible to colform, .1

Only simple, wellknown apparatus is relect 'tlietin on the cathodes in'sm'ooth, dense deposits of considerable thickness, free-from spongy or porousspots, and to melt the oath ode deposits with no" oxidation or drossing or the metal, thereby; greatly increasing the amount of tin finally iiecoveredin marketable quired, The operations are not complicated,

nor; are the reagents expensive; hence the process is economical to practice, inakingflt possible ,to treat solutions ofloyy grade whic'h would otherwise be Wasted or would have to H be concentrated at considerable expense,

The limpnrityfinetals removed fromjthe slolutioniby this process may be separated from, one another or given any desired subsequent treatment, and such treatment is facilitated fact that thejmet-alsfmay besepar'ated from the solution intw o" groupsiduring the treatment,

similar metals precipitated by the alkali suli rately from the selenium ,and o telliiriu m,

v v i y o, our hands; phide may he collected andtreated sep aand have pointed out in the annexed claims certain novel features of the invention, it

will be understood that various omissions,

substitutions and changes in the several steps of -the processand in its operation. may be made by those skilled in the alt without departing fro'm'the spirit oft-the invention.

Having thus described our invention, We claim: 1 '7 1, Procession purifying sodium stannate "solutions containing lead, copper, antimony, selenium and'tellurium, which consists inv agitating thcsolution with sodium sulphide in amountsto precipitate the lead and cop'- per,.s'eparating the precipitated lead and cop- "p erironi the solution. heating and agitating the, solution with t n in an oxid zable conditionin amounts to precipitate the antimony,

' selenium. and tellurium and separating, the

precipitatedmetals "from the solution.

2. Process forfremoving impurities from sodium'stannate solutions, which consists in adding j sodiui'n "sulphide tothe solution, agitating the jmix'ture to precipitate lead and copper, separating the precipitated j'met'als,

adding tin in an @oig'idiizahle fconditionto the.

solution While heated to a "temperature be- 1 tween de reesCfand its hoilin oint and V 1b 1 H ag t ti g o "pre mies h i ntifli ny S eniurn fand'telluriu n, and separating the precipitated metals fromjhe solution.

nate solutions, of removing lead and c pper by the e on, of tadium. u p then removing antimony selenium and, telrluriumihy the action oftinin oxidizable, condition an d jhe'at,.wherebyrthelsaidlead and copper may be recovered separatelyfrom the said antimony selenii m and 'tellurium, I

4. P ocess t'orpurifyingalkaIi rnetal stannate solutions, which Icfonsists in agitating the solut ion ivith all ralimetal sulphides separat ing tlie precipitatedimpurities from solution, heating theisolutionjto a temperaturebetxveen "degrees LQ and its boiling point and agitating iti vith tin in an ;oXi di zableg con ditiom, and separating the {precipitated "impuriti es.

5; Process for remoying impurities tr'o'm a ka t l t nhe e s lu on w ich ba sists in adding alkali-metalsulphide/to the solution, the mixture to: precipiitate lead andcopper, separating the precipitated metals g adding l in an o xidizable conditionto; the solution, heatingrto, a temlpemtmte ne ;fl i-b ilii sjpi int a ita g...t p e ipi ate? the tim ny, s l n u and telluriunnand separating the precipi- V v s ,tated metals from the solution, Thus the lead and copp d r I In testimony'whereogf e have hereunto set gt. Julian.

3. I In the purification of alkalimetal Stan- 

